The type of a function call expression

December 13, 2023


… The type of the expression is the result type of F. A method invocation is similar but the method itself is specified as a selector upon a value of the receiver type for the method.

math.Atan2(x, y)  // function call
var pt *Point
pt.Scale(3.5)     // method call with receiver pt

We recently talked about method calls already, so we don’t need to expand much more on those.

The main thing I want to discuss here is the first sentence: “The type of the expression is the result type of F.”

This is probably intuitive, and we actually demonstrated it yesterday, but it’s worth calling out explicitly, I think.

Given a function type of func (int, int) int, the type of the expression is the result type int.

So what about a function type of func() (int, error)? What is the type of the expression calling it? Well, it’s (int, error). That is, the expression resolves to multiple values, each of a distinct type (int and error respectively).

And this is where the rule we discussed yesterday comes in, that (except for a mystery exception not yet discussed) you can only use a function call as an argument to a function, when it returns a single value only.

Quotes from The Go Programming Language Specification Version of August 2, 2023

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Refresher on methods

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